High coupling efficiency is important for a light emitting device comprising a light emitting part and an optical waveguide system such as an optical fiber and optical waveguide and outputting light from the light emitting part via the optical waveguide system. The coupling efficiency is based on the power ratio of the incident light to the optical waveguide system and the guided light. Here, the coupling efficiency is used to mean the ratio in power of the guided light to the light generated in the light emitting part.
In order to improve the coupling efficiency, it is important to minimize the height difference between the luminous point of the light emitting part and the light incidence part of the optical waveguide system. Generally, a lens is provided between the light emitting part and optical waveguide system to collect and guide light emitted from the light emitting part into the light incidence part of the optical waveguide system for further improving the coupling efficiency.
However, when a light emitting part, a lens, and an optical waveguide system are mounted to constitute a light emitting device, generally, there will be difference in height (height difference) between the luminous point of the light emitting part and the center of the light incidence part of the optical waveguide system. The coupling efficiency will be low unless the height is adjusted.
For example, when a light emitting device is composed of an optical semiconductor device as the light emitting part, a lens, and an optical fiber as the optical waveguide system, the optical semiconductor device, lens, and optical fiber are mounted in this order so that the lens and optical fiber can be adjusted in height with respect to the luminous point of the optical semiconductor device, thereby preventing the coupling efficiency from deteriorating due to height difference of the luminous point upon mounting.
On the other hand, in a light emitting device comprising multiple light emitting parts and multiple optical waveguides corresponding in number to the light emitting parts as the optical waveguide system instead of an optical fiber (a light emitting part and an optical waveguide corresponding to the light emitting part are collectively termed a channel), the light emitting parts are subject to variation in mounted height, and the light incidence part of the optical waveguide in each channel should be adjusted in height.
In the above case, the same assemble order as the structure consisting of a light emitting part and an optical fiber as the optical waveguide system can be used to reduce height difference upon mounting between the luminous point of the light emitting part and the corresponding optical waveguide in one channel. However, since the optical multiplexer is already mounted, it is difficult to adjust the height difference upon mounting of the luminous point of the light emitting part using the optical multiplexer so as to match the height of the light incidence part of the optical waveguide corresponding to the light emitting part in the other channels.
Not only variation in height among the luminous points of the light emitting parts but also variation in height among multiple optical waveguides formed in the optical multiplexer should be adjusted. Without such adjustment, the average coupling efficiency between multiple light emitting parts and the optical multiplexer deteriorates.
In order to ameliorate the aforementioned deterioration in coupling efficiency between multiple light emitting parts and an optical multiplexer due to height difference between the luminous point of the light emitting part and the optical waveguide in each channel, an invention is disclosed in which a lens is interposed between an optical semiconductor device as the light emitting part and the optical multiplexer and the position of the lens is three-dimensionally adjusted in each channel to improve the coupling efficiency (Patent Literature 1). For mounting, a lens is mounted on the mechanism part for three-dimensional movement, the lens is moved to the optimum position by the mechanism part, and the mechanism part is fixed by solder melted by a heater.